Selective bird feeders are well known in the art and are designed to limit the maximum size of a bird or animal which can access the seed in the feeder. The reasons for excluding certain birds may be many. Thus, as disclosed in U.S. Pat. No. 3,241,525, there is provided a selective bird feeder which is specific to cardinals. As taught by this patent, a favorite seed of cardinals is the sunflower seed; this seed is also popular with both smaller and larger birds.
Some larger birds will also access the seed and many such birds including crows, grackles, bluejays and the like are considered by some people to be undesirable.
A further problem associated with bird feeders is marauders which gain access to the seeds. In particular, squirrels are well known for their ability to reach the seed in a bird feeder and to devour the same. Many approaches have been tried to discourage or prevent squirrels from reaching the bird feeder, including various types of covers and baffles on poles. These seldom work as the squirrels have shown great ingenuity in overcoming such devices.
Some of the attempted solutions to the problem are disclosed in the prior art such as exemplified by U.S. Pat. No. 4,646,686 to Furlani which teaches a movable shroud. U.S. Pat. No. 3,145,690 to Bachman describes a bird feeder in which an inverted cylindrical hopper is suspended over a feeding pan; a bird perch surrounds the pan and is attached to a conical shroud. Both the perch and the shroud are supported by a compression spring whereby heavier birds or mammals on the perch cause the shroud to move downwardly.
Another shroud arrangement is shown in U.S. Pat. No. 3,126,870 wherein a cylindrical shroud surrounds a hopper and is mounted for rotation about a vertical axis under the bias of a weight.
While all of the above references disclose shroud type arrangements, such devices have not appeared to have received commercial acceptance in the marketplace. It might be surmised that this is due to the fact that some of the arrangements are relatively complicated and/or expensive to produce.